A unified prediction framework of the hydration, strength, and sustainability of cement–slag concrete integrating ultrasonic pulse velocity

Previous studies on slag-blended concrete largely rely on data-driven approaches that lack explicit mechanistic links among hydration, mechanical performance, and sustainability, limiting interpretability. To address this issue, this study proposes a unified predictive framework for cement–slag concrete by integrating established hydration kinetics, gel–space ratio–based strength prediction, ultrasonic pulse velocity (UPV) correlation, and sustainability assessment. The cement hydration and slag reaction degrees are calculated using kinetic equations with parameters calibrated by isothermal calorimetry and kept constant across mixture proportions, enabling consistent hydration prediction. The compressive strength and UPV are then predicted on the basis of the gel–space ratio theory, achieving high accuracy, with correlation coefficients of 0.98 and 0.99, respectively. A combined material–carbon cost analysis further reveals that slag-blended concrete generally maintains economic advantages under increasing carbon prices, while rising slag prices may reduce or offset this benefit. Overall, the framework provides a transparent and transferable tool that links hydration-driven microstructural development to mechanical performance and sustainability, supporting rational low-carbon concrete design under evolving economic and policy conditions.